Ultrasonic enhancement of antibiotic action on Escherichia coli biofilms: an in vivo model

Biofilm infections are a common complication of prosthetic devices in human s. Previous in vitro research has determined that low-frequency ultrasound combined,vith aminoglycoside antibiotics is an effective method of killing biofilms. We report the development of an in vivo model to determine if ult rasound enhances antibiotic action. Two 24-h-old Escherichia coli (ATCC 107 98) biofilms grown on polyethylene disks were implanted subcutaneously on t he backs of New Zealand White female rabbits, one on each side of the spine . Low-frequency (28.48-kHz) and low-power-density (100- and 300-mW/cm(2)) c ontinuous ultrasound treatment was applied for 24 h with and without system ic administration of gentamicin. The disks were then removed, and the numbe r of viable bacteria on each disk was determined. At the low ultrasonic pow er used in this study, exposure to ultrasound only (no gentamicin) caused n o significant difference in bacterial viability. In the presence of antibio tic, there was a significant reduction due to 300-mW/cm(2) ultrasound (P = 0.0485) but no significant reduction due to 100-mW/cm(2) ultrasound. Tissue damage to the skin was noted at the 300-mW/cm(2) treatment level. Further development of this technique has promise in treatment of clinical implant infections.